Journal of Geosciences, Osaka City University Vol. 47, Art. 4, p. 39-53, March, 2004

Textural, Mineralogical and Microfacies Characteristics of the Lower Paleogene Succession at the Valley and Regions, Central

1 Ibrahim Mohamed GHANDOUR1,2, Abd EI-Monem T. ABD EL-HAMEED , 2 Mahmoud FARIS 1, Akmal MARzoUK I and Wataru MAEJIMA

I Department of Geology, Faculty of Science, University, 31527, Tanta, Egypt 2Department of Geosciences, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan

Abstract Four lithostratigraphic successions covering the Early Paleogene time have been measured and sam­ pled at the Nile Valley and Kharga Oasis areas in central Egypt. They include the Early-Late Paleocene upper Dakhla Shale and the Tarawan Chalk, and the Late Paleocene-Early Eocene Esna Shale. There is no marked variation between the grain size distribution of the Dakhla and Esna shales. They are generally composed of medium and coarse silts with small amounts of sand and clay. XRD analysis revealed the dominance of smectite with relatively low contents of kaolinite and illite and sporadic occur­ rence of palygorskite. Smectite was formed under warm semi - arid climatic conditions. Kaolinite, on the other hand, was formed under tropical to subtropical humid conditions. The relative proportions of smectite to kaolinite are controlled by the hydraulic sorting which concentrates kaolinite in the nearshore and shallow areas and drifts the smectite to deeper settings. The non-clay minerals are dominant by calcite with lower contents of quartz and local occurrences of feldspars. The high calcite content is consistent with the abundant calcareous fossils in the studied sediments. Dakhla Shale contains high carbonate contents and this is attributed to the high carbonate productivity and reduction of the detri­ tus influx during a period of sea level highstand. On the other hand, low carbonate contents of the Esna Shale was attributed to the dilution by high terrigenous influx during sea level lowstand. Petrographic examination of the Tarawan Chalk sediments and the interbedded limestones within the Dakhla Shale has led to the identification of four carbonate microfacies. These microfacies are: mud­ stone/wackestone, wackestone, wackestone/packstone and packstone. Dissolution of skeletal grains and infilling with iron oxides and neomorphic calcite are the dominant diagenetic features.

Key-words: Dakhla Shale, Esna Shale, Tarawan Chalk, Nile Valley Facies, clay minerals.

gross lithologic similarities and they belong to the same Introduction facies type (Nile Valley Facies) (Issawi, 1972). The lower Paleogene succession of the Nile Valley Lower Paleogene sediments were deposited over facies has attracted the attention of several geologists. large areas of Egypt as far south as the border of Sudan. Most of the previous studies were interested in the litho­ They are widely distributed in the Eastern and Western and biostratigraphic aspects (Said, 1962; 1990; Strougo, Deserts, Nile Valley, Gulf of area and Sinai. 1986; Speijer and Schmitz, 1998; Faris et aI., 1999 and Among these areas, the lower Paleogene sediments at others) and the mineralogical characteristics of the suc­ the Central Nile Valley and the Kharga Oasis display cession (Marzouk, 1985; Soliman et aI., 1989; Tantawy 40 Texture, mineralogy and microfacies of the Lower Paleogene succession, central Egypt

et a!., 2001). However, no previous studies have been uously except for short intervals (Said, 1990). done on the textural characteristics and the carbonate The lower Paleogene succession of the Nile Valley contents of the lower Paleogene sediments in this area. facies forms a tripartite subdivision arranged in ascend­ The present study aims at discriminating the lower ing order as the upper Dakhla Shale (Said, 1962), the Paleogene shales on the basis of their textural and min­ Tarawan Chalk (A wad and Ghobrial, 1965) and the Esna eralogical attributes, identifying the different microfa­ Shale (Zittel, 1883) (Fig. 1). These sediments were cies of the carbonate rocks, shedding light on the pale­ deposited in inner to middle shelf settings. oproductivity and paleoclimatic conditions that prevailed The Dakhla Shale was first described by Said during Early Paleogene time and their influence on the (1962) to describe the 130 m of shale succession over­ sediment composition. lying the upper Cretaceous phosphate bearing the Duwi Formation and underlying the Tarawan Chalk at the Mut Background and Lithologic Subdivisions location, . Generally, the age assigned to the Dakhla Shale is Late Cretaceous - Paleocene (Said, Said (1962) subdivided Egypt into two major tec­ 1962; Faris et a!., 1999). The basal part of the Dakhla tonic provinces, the tectonically deformed Unstable Shale (Upper Cretaceous-lowermost Paleocene) is not Shelf to the north (approximately to the North of lati­ represented herein. The studied upper part of the tude 28°) and the nearly horizontal and less deformed Dakhla Shale consists of 32-46 m of offshore fossilif­ Stable Shelf to the south. Intracratonic sedimentary erous greenish grey, calcareous shale, marl and argilla­ basins were developed on the southern Stable Shelf, ceous limestones. The studied interval of the Dakhla whereas pericratonic or rift basins were formed on the Shale ranges from Early Paleocene (NP2) to Late northern Unstable Shelf (E1- Hawat, 1997) Paleocene (NP7/8) (Faris et a!., 1999). In the Stable Shelf of Egypt, thick Phanerozoic suc­ The Tarawan Chalk (Awad and Ghobrial, 1965) cession was deposited in two broad intracratonic consists of fossiliferous, partly marly or chalky, yel­ depocenteres, the Upper Nile and the Dakhla basins. lowish white limestone of an outer shelf facies. The They are separated from each other by the Kharga and boundary between the Tarawan Chalk and the underly­ Dakhla basements, which are aligned in N -S and ing Dakhla Shale forms a significant regional discon­ WNW - ESE directions, respectively. These basins have formity recognized throughout southern and central evolved as a result of structural differentiation and sub­ Egypt. It corresponds to the boundary between the sidence of the rigid cratonic plate (El-Hawat, 1997). planktonic foraminiferal zones P3 and P5, and is Precambrian crystaJline basement highs surround these referred to as the .. Velascoensis Event" (Strougo, 1986; basins from the southern and eastern sides and they were Hermina, 1990). The Tarawan Chalk varies in thick­ the main source for terrigenous sediments during ness from 13 to 36 m. It is of Late Paleocene age (NP5­ Phanerozoic time. During Late Cretaceous, the Dakhla NP7/8 Zones) (Faris et a!., 1999). and Upper Nile basins were joined as a result of relief The Esna Shale (Zittel, 1883) is a thick succession inversion and subsidence of the Kharga high (El - Hawat, of green shale, enclosing marl and limestone intercala­ 1997). tions and lies between the two carbonate units, the The lower Paleogene sediments in the Upper Nile Tarawan Chalk at the base and the Thebes Formation at basin disconformably overlie the Cretaceous sediments the top. Like the Dakhla Shale, the Esna Shale is and are separated from it by thin intraformational con­ inferred to be accumulated mostly in inner to middle glomerate carrying reworked Cretaceous fossils (Said, shelf environments (Said, 1990). The age of the Esna 1990). Strougo (1986) related the stratigraphic rela­ Shale is Late Paleocene-Earl Eocene (NP7/8-NP11) tionships in the south and central Western Desert and (Faris et a!., 1999). in other areas to a large scale syndepositional tectonic disturbance, including faulting, which had led to marked Materials and Analytical Techniques changes of depositional pattern and he named this as Velascoensis Event. The materials of the present study were collected The Paleogene was ushered in by a transgression, from two different areas in Central Egypt; the ­ which pushed its way across the southern borders of Esna stretch on the eastern border of the Nile Valley Egypt into north Sudan. The maximum transgression and the Kharga Oasis. Four lithostratigraphic sections occurred during the Late Paleocene. After the Paleocene, (Fig. 1) were measured and sampled at G. El-Sheikh the sea kept retreating towards the north almost contin- Eisa (Qena region), G; El-Shaghab (Esna region), G. I. M. GHANDOUR et al. 41

32° ~N @ East Sahara Craton ,J.... ~~.~~ @ Nubian Shield \ ~~ ro,.... ~ Highs 30° I o?' ~~ \~ ~~ I~ ~ ...K"Troughs 1;;..- '0 Bahariya :~ Oasis LITHOLOGY 28° I Western I I Desert Shale 1 I Farafra Marl I Oasis 26° Argillaceous o...... 80 [JlZJKharga limestone km ·!~asis

24 @

II @ ·~---_~ ~YYE!~_---- SUDAN 26° 28° 34

30 m

20

10 40 39 o 34 - 35 35

23 30 30 30

Esna Shale 25 25 25 20

20 20 - 16 16 ~ H;:£i5:!r:1:;5------.J ~ Chalk 12

IS 10 10 Dakhla Shale 9 8

10 'rJ··~··~- •••••• 1 3 2 I

Fig. 1 Location map and the lithostratigraphic sections at the studied locations. 1) G. Teir/Tarawan, 2) G. Um El-Ghanayum, 3) G. El-Shaghab and 4) G. EI-Sheikh Eisa. The relative age and calcareous nannofossil zones are modified after Faris et al. (1999). The numbers at the right of the stratigraphic sections indicate sample numbers. 42 Texture, mineralogy and microfacies of the Lower Paleogene succession, central Egypt

Urn EI-Ghanayum and G. Teir/Tarawan (Kharga Oasis). sand fraction is determined by 63.um wet sieving, dried A Total of 165 samples were collected for the present and weighed. The mud fraction (silt and clay) was then work. The lithology, the number of samples and their placed in 1000 ml cylinder and the distilled water was locations in each section are shown in Fig. 1. The stud­ added until the volume was exactly 1000 m!. After ied sediments were analyzed for their textural (42 sam­ checking the temperature, several withdrawals at spe­ ples), mineralogical (18 samples) and carbonate micro­ cific times were taken (Folk, 1968). facies characteristics (13 samples). In addition, the The XRD analyses were carried out using a carbonate contents of the studied sediments were also RIGAKU RAD-IX -ray powdered Diffractometer with determined. Cu K a radiation and energy of 30 kV and lOrnA. The pipette method (Galehouse, 1971; Lewis and Small pieces (30 gm) of shale samples were dried and McConchie, 1994) is used here to determine the sand, finely powdered with agate mortar and pestle. The min­ silt and clay contents of the Dakhla and Esna shales. eralogical investigation was carried out on the bulk rock The sediments were easily disintegrated when soaked in and on the clay sized «2 .urn) fractions. For the bulk water. They were covered by 15% of H202 to remove rock mineralogy, the powdered samples were packed the organic matter and act as a dispersant agent. The into a cavity bearing glass slide (Hardy and Tucker,

Table 1 Results of the textural analysis.

Location Fm S. No Sand Silt Clay wt% wt% wt% <4<1:> 4<1:> 4.5<1:> 5<1:> 5.5<1:> 6<1:> 7<1:> 8<1:> >8<1:> Esna T-21 10 3 7 20 10 16 17 0 17 Shale T-15 1 3 19 64 6 1 1 0 6 c:: .-.--.---- ..._-_ .._------_.------.-- I::; T-13 4 15 45 20 3 3 0 2 7 '0 '"~ E-<. ~'" Dakhla T-6 3 27 22 38 2 1 2 2 3 Of-< Shale T-3 3 6 20 33 16 11 1 1 8 G-37 0 1 11 76 5 1 0 0 5 8 G-35 0 12 13 63 4 2 1 0 6 :::l 4 ;>., G-34 0 2 5 30 55 3 1 0 '"c:: Esna G-30 1 1 10 79 3 1 0 1 4 G-28 1 5 3 78 4 2 2 1 5 ..<::'" Shale C? G-26 7 2 6 11 68 1 1 0 4 ~ G-25 3 4 9 30 48 1 1 0 4 8 G-24 1 3 7 22 59 2 0 1 6 ;:J ------G-22 ------3 .------.--.------2 7 20 58 1 0 2 6 0 D. Sh G-12 1 1 6 14 67 4 0 2 5 S-67 10 7 7 53 14 1 1 2 6 S-66 2 9 17 51 7 5 1 0 7 S-64 2 4 16 58 2 9 0 0 8 S-62 1 8 5 46 22 8 2 1 7 S-59 2 5 9 68 3 6 0 2 6 S-54 1 5 5 20 5 18 11 21 16 .0 S-52 1 4 8 19 12 14 12 11 20 ..<::'"on Esna S-51 1 4 5 12 16 17 17 15 14 ..<::'" S-49 1 2 9 11 16 14 11 19 18 t1 S-47 1 1 0 12 6 32 35 0 12 ~ S-45 1 2 11 12 16 13 13 6 25 0 Shale S-44 4 6 10 13 14 18 19 9 8 S-42 2 3 16 16 9 14 9 15 17 S-37 1 3 3 1 8 39 34 1 9 S-36 0 3 7 81 0 3 0 0 6 S-33 5 4 7 75 3 0 0 0 6 S-32 2 4 2 14 37 28 1 4 7 S-25 7 3 2 75 4 1 0 0 7 E-31 1 6 15 35 37 0 0 1 6 E-28 3 3 8 21 62 0 0 0 4 '" E-26 1 3 8 35 44 0 0 0 7 iii'" Esna E-24 1 2 15 21 55 0 0 0 1 j2 E-22 1 4 9 41 36 0 0 0 7 '0 ..<:: E-20 8 3 10 46 21 1 1 0 9 t1 Shale E-19 6 3 9 67 5 1 2 0 7 ~ ------E-16 .------.---2 ------.--o 26 65 0 1 0 0 5 0 D. Sh. E-ll 5 11 69 6 0 0 0 1 8 D. Sh.: Dakhla Shale 1. M. GHANDOUR et a!. 43

1988). The slides are then scanned by XRD at a rate He] and after heating to 550°C. All slides were scanned of 1°/minute from 2° to 40° 2 e. For clay «2 ,urn) min­ at a rate of 1°/minute at a range from 2° to 30° 2 e. erals analysis, X -ray diffraction was undertaken on ori­ Minerals were identified by their characteristic reflec­ ented aggregates. Samples were completely dispersed tions as discussed by Moore and Reynolds (1989). The in diluted solution of calgon to avoid flocculation. The basic (001) reflection of glycolated smectite is 17 A clay fractions «2 ,urn) were separated by centrifugation. and the (00l) and (002) reflections of kaolinite are 7.16 Oriented samples of the clay «2 ,urn) fractions were pre­ A and 3.58 A, respectively. Illite was identified at 10 pared by carefully pipetting the clay suspension on a A and palygorskite at 10.5 A. The following peaks glass slide allowing the fractions to be homogeneously identify non-clay minerals: quartz, 4.26 A, K-feldspar, distributed. For determination of the clay mineral com­ 3.25 A, and calcite 3.04 A. Because the intensity of position, the oriented samples were X -ray scanned a diffraction pattern (generally expressed as peak height under four separate conditions: air-dried, after satura­ or peak area) of a mineral in a mixture is proportional tion with ethylene glycol, after treatment with warm 6N to its concentration, the relative proportions (semiquan-

Dakhla Shale Esna Shale

E-31

E-26

E-2-I

E-22

E-20 ::::

E-19 :

E-16

8-66 8-64 8-62

.c 0: ... Sand % .c: D 011 0: Silt % .c: ~ ~ ~ Clay 0/0 rj •

8-33 :­ 8-32 . 8-25 ..

-3

-3

-30

Fig. 2 Sand, silt and clay percent­ ages identified from the grain size analysis of the studied shales. 44 Texture, mineralogy and microfacies of the Lower Paleogene succession, central Egypt

titative in nature expressed as vol %) of the identified sification of Folk (1959) and the depositional textures minerals are roughly determined using their peak inten­ of Dunham (1962) are followed herein. sities using the Mac Diff 4.2.5 software. In the case of In addition, the carbonate contents of the studied bulk rock mineralogy, mineral abundances were deter­ sediments were also determined following the method mined using peak heights, whereas the integrated peak described in Lewis and McConchie (1994), which is areas of glycolated samples were used to determine the based on the digestion of carbonates using 1M HCl and relative abundances of the <2.um m fractions. The clay the back titration of the unused acid by 1M NaOH using fractions were measured using a formula: kaolinitel2.5 + phenolphthalein indicator. smectite + illite + palygorskite = 100% (Hardy and Tucker, 1988). Results The microfacies analysis were carried out on stained (Alizarin Red S) carbonate rocks of the lower Dakhla Grain-size distribution Shale and the Tarawan Chalk. The petrographic clas- The sand, silt and clay percentages determined by

G TcirfTarawan

~-- --A_-Jo_.Jn\'-f"~__I\__-lL T-ll

;:::::::=::::::=~,~==~~,~~~~~==::=:=:::::::~T-4 12 26 22

G Urn Et-Gbanayurn ~ ..s 1:. ..c: ll..

G-25

2 12 26 32

G El-5bagbab

8-67 8-58 8-52 8-48 8-24 8-8 8-5 I I 2 12 22 26

GEt-Sheikh Eisa

A E-34 A E-29 \.. I E-27 \. A E-24 Fig. 3 Representative X-ray diffractograms \. 1\ A J, E-8 of the lower Paleogene sediments. \... A A E-6 (A) bulk rock mineralogy and (B) 12 22 32 26 clay size «2 .um) fraction. I. M. GHANDOUR et al. 45

pipette analysis are shown in Table 1 and Fig. 2. The ates vertically without definite trend. The highest sand results of the textural analysis exhibit no marked tex­ peak (10%) was obtained from the upper Esna Shale at tural difference between the Dakhla and Esna forma­ G. El-Shaghab and G. Teir Tarawan. tions. The Dakhla and Esna shales are composed mainly Silt is the dominant size fraction. The Dakhla of coarse to medium silts with subordinate quantities of Shale has relatively higher silt contents than the Esna sand and clays. Sand fraction is recorded with rela­ Shale. The upper Dakhla Shale at G. Um El-Ghanayum tively lower values and never exceeds 10%. It fluctu- has the highest silt contents (94%), whereas the lowest

G-26 ~ T-4 ~ :~E ,,, ,, 2 7 12 h 22 27 28 28 G-25 8-67

~..A..-..-l.

,, , , ,, 17 22 27 2 1'2 17 22 h 28 28

~ :5 e 8-8 8-48 01 ..:.=

, 2 '1 12 22 17 22 i7 28 h 28

E-34 ~ 8-5 ~ 0- ~: .... _=h e ~ ~ ~s .. -----l = ~ ~: , =J::± 2 12 17 2 7 12 28 17 22 27 7 28 22 i7

E-8 "-- 1 .E-24 ~ : =:::~~ = w 2 7 12: 17 22 27 s= 12 28 2 7 28 1'7= 22 27

Fig. 3 Continued. 46 Texture, mineralogy and microfacies of the Lower Paleogene succession, central Egypt

value (73%) was obtained from the upper Esna Shale at However, the upper Dakhla Shale sediments contain G. Teir/Tarawan. The silt contents determined from the higher calcite contents than the sediments of the Esna Esna Shale sediments vary from 73 to 96%. A wide Shale. The Dakhla Shale sediments yield calcite with spectrum of different size classes ranging from very fine values ranging from 58%-97%, whereas the calcite con­ silt to coarse silt was observed from the studied sedi­ tents in the Esna Shale sediments range from 16% to ments. Among silt-size classes, 5

Table 2 Results of the XRD analysis.

Location Frn S. Bulk Rock Mineralogy Clay-size «2.urn ) Mineralogy No Phyll Qz Fels Cal Srn Ilt Palg Kao Qz Cal v% v% v% v% v% v% v% v% v% v% G.Teir/ D. T-ll - 3 - 97 59 17 24 F A Tarawan Sh. T-4 11 10 - 79 60 9 - 31 R F G. G-34 30 27 3 40 86 -- 14 R R UmEI- Esna G-26 32 22 3 43 84 - 7 9 R R Ghanayum Shale G-25 25 21 - 54 80 3 4 13 F F S-67 20 12 - 68 83 -- 17 R F G.EI- S-58 63 21 16 73 3 - 24 F R Shaghab Esna S-52 26 20 - 54 86 - 5 9 R R Shale S-48 68 32 - - 46 5 10 39 C - S-24 23 - 77 93 - 4 3 AA ------. ~ ~ ----.--._------.------~ ------D. S-8 24 16 2 58 35 7 - 58 F C Sh. S-5 5 11 85 46 18 - 36 AA E-34 4 9 - 88 66 34 -- R A G. El- Esna E-29 6 7 - 87 71 10 - 19 R A Sheikh Shale E-27 30 24 2 44 - - - - A E-24 20 12 2 66 67 11 22 F C Eisa ------_.---_.------D. E-8 - 3 - 97 86 - - 14 FA Sh. E-6 2 3 - 95 73 15 - 12 FA

A: Abundant, C: Common, F: Frequent, R: Rare, (-) not detected D. Sh: Dakhla Shale Phyll.: Phyllosilicates, Qz: Quartz, Fels.: Feldspars, Cal. Calcite, Sm.: Smectite, lit.: Illite, Kao.: Kaolinite I. M. GHANDOUR et al. 47

Fig. 4 Photomicrographs of the identified microfacies. (A) Wackestone microfacies, lower Tarawan Chalk at G. EI­ Shaghab. The broken planktonic foraminiferal tests are embedded within micrite. Note the iron oxide infilling and patches.X-50. (B) Wackestone microfacies, lower Tarawan Chalk at G. Um EI-Ghanayum, the benthic foraminiferal test is completely filled with iron oxides. X-125. (C & D) Wackestone/packstone microfacies, upper Tarawan Chalk, G. Urn EI-Ghanayum. X-125. Notice the rnicritized wall of benthic foraminiferal tests and the infilling by sparry calcite. (E & F) Packstone microfacies, upper Dakhla Shale, G. El- Shaghab, X­ 125. Most of the foraminiferal tests are filled with ferroan sparry calcite. 48 Texture, mineralogy and microfacies of the Lower Paleogene succession, central Egypt

rocks (Dunham, 1962), four microfacies were identified. patches and dark ferruginous spots are scattered ran­ They are: mudstone/wackestone, wackestone, wacke­ domly. stone/packstone and packstone. Photomicrographs of The wackestone microfacies (Fig. 4A and B) is the the different microfacies are shown in Fig. 4. common microfacie of the middle part of Tarawan The mudstone/wackestone microfacies (Fig. 4A) is Chalk at G. El-Shaghab, G. Um EI-Ghanayum and G. recorded from the upper part of the Tarawan Chalk at EI-Sheikh Eisa. Microscopically, the framework of this G. EI-Shaghab. This facies is made up of dense and microfacies is composed of moderately sorted skeletal cloudy cryptocrystalline non -ferroan calcite contain ing particles (25%) randomly scattered throughout the some skeletal fragments « 10%) dom inated by frag­ micrite. The skeletal particles include planktonic and ments of foraminiferal tests. Foraminiferal chambers benthic foraminifera. Most foraminiferal tests are par­ are partially filled with iron oxides. Few iron oxide tially or completely filled or replaced with recrystallized

Table 3 The carbonate contents of the studied sediments.

Location G.Teir G. Urn EI- G. EI-Shaghab G. El-Sheikh /Tarawan Ghanayum Eisa Car. Car. Car. Car. Car. Formation No. S. No. S.No. S.No. S. No. s. wl% wt% wl% wt% wt% T-23 15 G-39 9 S-67 26 S-40 60 E-34 65 T-22 21 G-38 t2 S-66 1.7 S-39 53 E-33 42 T-21 24 G-37 8 5-65 16 S-38 7 E-32 37 T-20 99 G-36 7 5-64 17 S-37 8 E-31 24 G-35 38 S-63 9 S-36 42 E-30 33 G-34 12 S-62 14 S-35 42 E-29 47 G-33 6 S-61 4 5-41 5 E-28 12 G-32 19 5-60 10 5-34 49 E-27 10 G-31 14 5-59 22 5-33 34 E-26 10 G-30 17 S-58 7 S-32 5 E-25 16 G-29 16 5-57 13 5-31 14 E-24 13 G-28 21 5-56 11 5-29 54 E-23 21 G-27 54 S-54 4 5-28 30 E-22 31 Esna Shale G-26 35 5-53 22 5-27 18 E-21 21 G-25 20 5-52 23 5-26 18 E-20 12 G-24 17 5-51 6 5-25 28 E-19 34 G23 21 5-50 10 5-24 73 E-18 36 G-22 24 5-49 8 5-23 55 E-17 50 G-21 51 5-48 6 5-22 49 E-16 43 G-18 56 5-47 1 5-2l 49 E-15 82 5-46 14 5-20 64 5-45 18 5-19 66 5-44 28 5-18 79 5-43 5 5-17 76 5-42 6 5-16 73 Tarawan T-19 96 G-16 98 5-13 90 E-14 91 Chalk T-18 84 G15 89 5-12 93 E-13 95 G-14 88 E-12 96 T-17 77 G-13 16 S-10 85 E-ll 66 T-16 92 G-12 11 S-9 19 E-IO 87 T-15 30 G-ll 22 S-8 28 E-9 84 Dakhla T-14 23 G-1O 23 5-6 70 E-8 70 T-13 27 G-9 26 5-5 68 E-7 86 T-12 29 G-8 13 5-4 80 E-6 86 Shale T-1J 85 G-7 43 S-3 69 E-5 75 T-IO 19 G-6 34 S-l 64 E-4 74 T-9 23 G-5 49 E-3 65 T-8 35 G-4 57 E-2 60 T-7 57 G-3 54 E-l 55 T-6 34 G-2 77 T-5 37 G-l 79 T-4 48 T-3 29 T-2 52 Car.: Carbonate content. I. M. GHANDOUR et al. 49

sparry calcite or iron oxides. The walls of many tests Porosity ranges from low to moderate as evidenced by are micritized. Porosity is generally low to moderate the presence of small irregular vuggy pores. and represented by small vuggy pores. The packstone microfacies (Fig. 4E and F) is The wackestone/packstone microfacies (Fig. 4C recorded from the limestone intercalations within the and D) is recognized from the lower Tarawan Chalk at Dakhla Shale at G. EI-Shaghab. This microfacies is G. EI-Shaghab and the upper Esna Shale at G. EI­ mainly composed of moderately sorted and well packed Sheikh Eisa. It is made up of skeletal particles (45­ planktonic and benthic foraminiferal tests showing point 50%) of planktonic foraminiferal tests packed in micrite. and grain -contact. Infilling with sparry calcite and iron The foraminiferal chambers are generally filled with oxide as well as the test wall micritization are the com­ sparry calcite and in some cases with iron oxides. mon features affecting the skeletal particles. The fer­ Micritization is a common phenomenon that affected roan calcite is the dominant calcite type. Porosity is some test walls. Large neomorphic ferroan and non­ generally moderate and represented by irregular vugs ferroan sparry calcite is observed filling some fractures. and large intragranular pores.

G TeirfTarawan G Urn EI-Ghanayurn G EI-Shaghab GEl-Sheikh Eisa 0 50 100 0 50 100 0 50 100 0 50 100 T-23 G-39 8-67 E-34 G-38 8-66 E-33 G-37 8-65 E-32 8-64 G-36 E-31 8-63 G-35 8-62 E-30 G-34 8-61 E-29 G-33 8-60 E-28 T-22 8-59 G-32 8-58 E-27 G-31 E-26 ClI 8-57 ~ G-30 8-56 E-25 8-S4 rJJ-= G-29 E-24 8-53 G-28 8-52 E-23 G-27 8-51 E-22 T-21 8-50 G-26 E-21 ~ 8-49 G-25 E-20 =~ 8-48 f;l:;l G-24 8-47 E-19 G-23 8-46 E-18 8-45 G-22 E-17 8-44 G-21 8-43 E-16 T-20 G-18 8-42 E-15

T-17 G-13 8-10 E-ll T-16 G-12 E-lO T-15 8-9 G-ll T-14 E-9

ClI T-13 8-8 ~ E-8 T-12 G-9 rJJ-= T-Il E-7 G-8 8-6

~ T-tO G-7 E-6 ::c,.:;:: T-9 ~ G-6 8-5 Q T-8 E-5

T-7 G-5 Fig. 5 Vertical variations of the E-4 To{; 8-4 G-4 carbonate contents in the T-5 E-3 Dakhla and Esna shales at G-3 the different local i ties. 8-3 T-4 Note the higher carbonate G-2 E-2 T-3 content of Dakhla Shale T-2 G-! 8-1 E-! relative to the Esna Shale. 50 Texture, mineralogy and microfacies of the Lower Paleogene succession, central Egypt

Carbonate contents The proportions of the carbonate content have a Discussion wide spectrum of values ranging from 0 to 98 % (Table 3 and Fig. 5). Generally, the Dakhla Shale sediments The lower Paleogene sediments in central Egypt have higher carbonate contents than those of the Esna contain abundant and highly diversified planktonic Shale. The average values of carbonate content foraminifera and calcareous nannoplanktons (Faris et recorded from the Dakhla Shale are 39% (range 11­ a\., 1999), suggesting deposition in open marine inner 79%) at G. Urn El-Ghanayum, 43% (19-92%) at G. to middle shelf environments. Sea level fluctuations, Teir/Tarawan, 60% (19-85%) at G. EI-Shaghab, and climate, paleogeography, basin physiography and sedi­ 74% (55-87%) at G. El-Sheikh Eisa. ment supply have significant signatures on the lower The Esna Shale sediments have relatively lower Paleogene sediment characteristics in central Egypt. carbonate contents. They range from 10-82% (averag­ ing 32%) at G. E1-Sheikh Eisa, from 1-79% (averag­ Depositional processes ing, 27%) at G. EI-Shaghab, from 6-56% (averaging, The studied sediments are exclusively enriched in 23%) at G. Urn El-Ghanayum, and from 15-99% (aver­ silts with subordinate quantities of clays and sands. The aging, 40%) at G. Teir/Tarawan. high percentages of silts and clays would suggest a dep­ The acid insoluble residue determined for the osition from suspension. The present study shows the Tarawan Chalk varies from 4% to 9% (averaging 6%) independence of fine grain size distribution on the water at G. El-Sheikh Eisa, from 7% to 10% (averaging 9%) depths. The lower Paleogene sediments at the Esna area at G. El-Shaghab, from 2% to 12% (averaging 8%) at (G. El-Shaghab) were deposited under relatively shal­ G. Urn El-Ghanayum, and from 4% to 16% (averaging, lower conditions than other areas (Said, 1990), (Fig. 6). 10%) at G. Teir/Tarawan. Microscopic examination of However, there is no difference between the grain size the acid insoluble residues revealed the presence of distributions in all of the studied sediments. Generally, detrital and fine sand- and silt- sized quartz grains, siliciclastic sediments are delivered to the basin from clays, few pyritized fossils, few iron oxides, and rare the nearby land areas. The coarse sediments are con­ agglutinated foraminifera. centrated in the nearshore areas and the fines are drifted to the deeper sites. Unlike sands, deposition of muds is not primarily governed only by particle size, water depths and flow velocities. There is no need to assume 32° that muds were necessarily deposited under conditions of lower current velocity, lower wave activity or greater water depth. Those substantial amounts of mud can 30° • indeed be deposited in energetic environments when suspensions are concentrated enough (McCave, 1984). McCave (1984) distinguished three main processes for the deposition of fine grained sediments: 1) re - sedi­ rahariya mentation processes including all processes that move Farafra sediments downslope over the sea floor; 2) normal bot­ tom currents (contourites) that erode, transport and Qena deposit sediments on the sea floor and 3) pelagic set­ ... tling through the water column. However, in the sea 25" ff· water, muds are easily flocculated and behave as aggre­ g... I . gates rather than individual particles. Therefore, floc­ culation played the main role in the deposition of Dakhla and Esna shales.

E- - - Paleoshore-lineI Carbonate paleoproductivity The studied lower Paleogene sediments were Fig. 6 Early Paleogene paleoshoreline (Said, 1990). Note that the Qena area was relatively deeper deposited under different phases of carbonate produc­ than the Esna and Kharga during Early tivities. Most of calcareous materials include remains Paleogene. of calcareous fossils and calcite. The abundance of car- 1. M. GHANDOUR et al. 51

bonate in the Dakhla Shale sediments is attributed to mineral in the studied sediments, whereas low illite con­ the high carbonate productivity during periods of tents were obtained. Palygorskite occurred with subor­ reduced terrigenous influx. The Dakhla Shale sediments dinate amounts at specific horizons. Neither chlorite were deposited during sea level highstand (Luning et aI., nor mixed-layer clays were found in the studied shales. 1998), which led to the reduction of terrigenous influx, It is worthy mentioning that, clay minerals of the allowed calcareous organisms to flourish and resulted in studied sediments are of detrital origin and there is no increasing carbonate production. On the other hand, the evidence for the influence of diagenesis. Hoffman and relatively low carbonate contents obtained from the Hower (1979) referred to the mineralogical criteria for Upper Paleocene-Lower Eocene Esna Shale were shale diagenesis, which include: i) conversion of smec­ related to high terrigenous influxes and to the syn - and tite to illite through mixed layer, ii) the appearance of post-depositional dissolution of readily dissolved plank­ chlorite, and iii) disappearance of K-feldspars as a tonic organisms. The Esna Shale was deposited during result of decomposition. Furthermore, the presence of sea level lowstand (Said, 1990), during which high smectite implies that the clay minerals are not trans­ amounts of terrigenous sediments were delivered to the formed due to burial diagenesis (Charnley, 1989). basin. Smectite, the dominant clay mineral in the studied The lower Paleogene sediments were laid down in sediments, indicates that the source area had experi­ inner to middle shelf environments. These sites are tol­ enced a warm climate with alternating pronounced dry erated by varieties of calcareous fauna which con­ and less pronounced wet seasons. The smectite has been tributed well in the carbonate composition of the stud­ transported to the ocean either in river run-off during ied sediments. The productivity of the calcareous wet seasons and/or as aeolian particles during dry sea­ microinvertebrates is influenced by numerous water­ sons. Hallam et al. (1991) has referred to the vol­ mass properties such as temperature, pressure, density, canogenic smectite, being derived directly from the nutrients, salinity, light penetration, oxygen and other weathering and alteration of volcanic materials. physical, chemical and biological factors (Luning et aI., Although the Late Paleocene-Early Eocene time is char­ 1998). Most of calcareous nannoplanktons and plank­ acterized by massive eruption of flood basalts (Eldholm tonic foraminifera have their highest abundance in areas and Thomas, 1993), the volcanogenic origin of smectite of ocean upwelling (Soutar et aI., 1981). Upwelling would be excluded due to the absence of associated process is important for planktonic organisms as it accessory minerals like biotite, sphene, and relict glass brings the nutrient-rich subsurface water to the photo­ shards. High abundance of smectite was recorded from synthetic layer. Upwelling process also controls the the lower Paleogene sediments at other localities in cen­ bottom environment through enhanced downward flux tral Egypt (Marzouk, 1985; Soliman et aI., 1989). of organic matter. The Dakhla Shale sediments were Kaolinite, the second abundant clay mineral deposited in environments with enhanced upwelling encountered in the studied sediments, has resulted from processes, whereas reduced upwelling intensities had the chemical weathering of acidic igneous and meta­ dominated during the deposition of the Esna Shale. morphic rocks or their detrital weathering products under tropical to subtropical humid climatic conditions Factors controlling mineralogical composition (Hendriks, 1985; Marzouk, 1985; Chamley, 1989). The studied lower Paleogene sediments are domi­ Illite typically forms under conditions completely nated by calcite, phyllosilicates, quartz and few amounts different from those under which kaolinite and smectite of feldspars (Table 2). Calcite and phyllosilicates show are formed. It typically forms in soils with little chem­ opposite behaviour. This may explain the carbonate ical weathering in cold and/or dry climates, and in areas dilution by the land derived terrigenous materials. The of high relief where physical erosion is predominant. dominance of calcite over other minerals in the bulk The relatively lower illite contents of the studied shales fraction is consistent with the high abundance of cal­ were produced by physical erosion of illite-bearing careous fossils (Faris et a\., 1999). source rocks. The presence of illite with quartz sug­ The clay minerals distributions in the lower gests high detrital input in dry climates. Paleogene sediments reflect the climatic conditions and The lower proportions of the palygorskite deter­ the weathering processes at the source area as well as mined from the lower Esna Shale sediments at G. Um the differential hydraulic sorting during transportation EI-Ghanayum and G. El-Shaghab developed on vari­ and deposition. Smectite dominates the clay mineral ous crystalline substrates such as granites and green­ assemblages. Kaolinite is the second abundant clay schists provided that hydrolysis and evaporation condi- 52 Texture, mineralogy and microfacies of the Lower Paleogene succession, central Egypt

tions were strong enough (Charnley, 1989). Petrographic examination of the Tarawan Chalk and the Apart from the climatic controls, which affect clay limestone interbeds in the upper Dakhla Shale enables mineral formation, the relative abundance of kaolinite to identify four microfacies. These microfacies are and illite comparing to smectite is clearly influenced by mudstone/wackestone, wackestone, wackestone/pack­ hydraulic sorting and relative sea-level changes. The stone and packstone microfacies. Dissolution of origi­ lower proportions of kaolinite and illite relative to smec­ nal test wall and replacement and infilling by iron tite in the studied sediments would be explained as oxides and recrystallized calcite were the main diage­ kaolinite and illite tend to concentrate in relatively netic features. The Dakhla Shale sediments especially near-shore shallow water settings, reflecting their those at Qena region have high carbonate contents rel­ coarse-grained nature and their strong tendency to floc­ ative to sediments of the Esna Shale. The water depth, culate compared to smectite, whereas smectite tends to sediment supply, sea-level changes and the carbonate settle as finer particles in deeper offshore settings productivity were the major controls on the carbonate (Raucsik and Merenyi, 2000). As the studied sediments accumulations of the studied sediments. represent deposition in the distal deeper part of the basin, it is expected to find higher concentrations of Acknowledgements kaolinite and illite with lower smectite abundances at the proximal shallower settings. Moreover, detrital This work is based on a part of the M.Sc. work of smectite in marine sediments increases during sea -level the first author carried out at Tanta University, Tanta, highstand periods, whereas kaolinite and mica increase Egypt. Additional data on the rock mineralogy have during lowstand periods. The presence of abundant been added during his study at Osaka City University. smectite is generally linked to transgressive seas The first author would like to acknowledge the Japanese (Tantawy et aI., 2001). Ministry of Education, Science, Culture and Sports for supporting his study at Osaka City University. The Summary and Conclusions authors would like to thank Prof. N. Aikawa and Dr. K. Shinoda, Osaka City University for facilitating the use Four lithostratigraphic sections covering the Early of XRD instrument. The authors are thankful to Dr. T. Paleogene time were measured and sampled at the Nile Nakajo, Osaka Museum of Natural History and an Valley and the Kharga Oasis, Central Egypt. The stud­ anonymous reviewer for reviewing the manuscript. ied interval includes two shale-dominated formations; the upper Dakhla Shale and the Esna Shale separated References by the carbonate dominated Tarawan Chalk. The grain­ size distribution, mineralogical composition, total car­ Awad, G. H. and Ghobrial, M. G. (1965) Zonal stratig­ bonate-contents and the carbonate microfacies have raphy of the Kharga Oasis. Geol. Surv. Egypt, 34, been determined. The grain - size distributions of the 77 pp. Dakhla and Esna shales are quite similar to each other Chamley, H. (1989) Clay sedimentology. Berlin, and are dominated by silt (medium and coarse silt) with Springer-Verlag, 623 pp. generally small amounts of sand and clay. Mineralogical Dunham, R. J. (1962) Classification of carbonate rocks analysis carried out by XRD revealed the presence of according to depositional textures. In: Classification smectite, k3.olinite, illite and palygorskite as the princi­ of Carbonate Rocks (Ham, W. E. ed.), AAPG pal clay minerals, and calcite, quartz and K -feldspars Mem., 1, 108- 121. as non -clay minerals. Calcite is the most abundant El - Hawat, A. S. (1997) Sedimentary basins of Egypt: non -clay mineral and this is consistent with the high An overview of dynamic stratigraphy. In: African calcareous fossil content of the studied sediments. basins, Sedimentary basins of the world, 3 (SeJley, Smectite, the most abundant clay mineral, has been R. C. ed.) Amsterdam, Elsevier, 39-85. formed under warm climatic conditions with alternation Eldholm, O. and Thomas, E. (1993) Environmental of pronounced dry and less pronounced wet seasons. impact of volcanic margin formation. Earth Planet. The smectite abundance relative to kaolinite was gov­ Sci. Lett., 117, 3l9?329. erned by dominant hydraulic segregation during trans­ Faris, M., Abd El-Hameed, A. T., Marzouk, A. M. and portation. Smectite was drifted to deeper settings, Ghandour, 1. M. (1999) Early Paleogene calcareous whereas kaolinite was concentrated in the proximal nannofossil and planktonic foraminiferal biostratig­ nearshore and/or non-marine parts of the basins. raphy in Central Egypt. J. N. lb. Geol. Pald.ont. I. M. GHANDOUR et al. 53

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Manuscript received August 14, 2003. Revised manuscript accepted December 15, 2003.